1. Field of the Invention
The present invention relates to a novel polyol and a process for producing a rigid polyurethane foam derived from the polyol.
2. Description of the Prior Art
A polyurethane is usually produced by reacting an active hydrogen compound such as a polyol with a polyisocyanate. The typical polyol is a polyetherpolyol produced by bonding an intiator to an alkyleneoxide. The initiator is a compound having two or more active hydrogen atoms. The typical active hydrogen atom is hydrogen atom in hydroxyl group or amine group.
The polyurethane foam as one kind of polyurethane is classified into a flexible foam and a rigid foam. The polyol for the flexible foam is mainly a polyol having 2-4 of hydroxyl groups. The polyol for the rigid foam is mainly a polyol having up to 8 of hydroxyl group. The initiator used for producing the polyol for the rigid foam is mainly a saccharide or a mixture of a saccharide and an alcohol having 3 or 4 OH group such as glycerin. Sometimes, an aromatic initiator is used in view of an application.
The rigid polyurethane foam produced by using a polyol obtained by bonding an aromatic initiator to an epoxide may have the improved rigidity and thermal flexibility.
The typical aromatic initiator is novolak type initiator obtained by condensing phenol and formaldehyde. Sometimes, aromatic amine is added. The initiator obtained by condensing an aldehyde, a phenol and aniline is disclosed in U.S. Pat. No. 3,222,305 and the initiator obtained by condensing an aldehyde, a phenol and/or aniline and a nonaromatic primary amine is disclosed in British Pat. No. 1,061,210. Thus, these initiators are not satisfactory thereby requiring certain improvement. For example, the known initiators have problems of dehydration and gelation.
When an epoxide is bonded to the initiator, a diol is produced by the reaction of the epoxide with water when water is present as an impurity. It has been known to cause deterioration of physical properties of the foam in the presence of the diol. On the other hand, the aldehyde-phenol-aniline condensate includes a compound obtained by crosslinking phenyl group by methylene group. Thus, the product also includes a compound having methylol group which remained without the crosslinking. It is quite difficult to completely eliminate the methylol group nevertheless a dehydration is caused under the epoxide adduct reaction. When the crosslinking with the aldehyde is locally concentrated, the polymeric condensation is easily resulted and the gelation is resulted and the adduction of the epoxide is not easy. Moreover, in the production of the condensate disclosed in the latter prior art reference, the reaction is not stoichiometrically performed and the object condensate is not easily produced at high yield. Moreover, there is a problem of uneasy availability of an initiator having a desired number of functional groups.
In order to improve the condensate disclosed in the reference, an initiator is produced by reacting the components except replacing the primary amine to an alkanolamine and a polyol is produced by using the initiator and a polyurethane foam is produced by using the polyol to evaluate the polyol. The main reaction of the aldehyde, aniline and the alkanolamine is considered as Mannich reaction. It is considered that the aniline having alkanolaminomethylene group is produced by reacting the aldehyde and the alkanolamine reaction product with p- or o-site of the aniline. However, the Mannich reaction is not effectively performed but a methylene crosslinking reaction between aniline molecules is mainly performed. It has been found to be difficult to overcome the problem.
On the other hand, the polyol produced by using the aldehyde-phenol-alkanolamine reaction product as an initiator is known and is disclosed in U.S. Pat. No. 3,297,597. However, the condensate of the three components is not satisfactory. That is, the reaction velocity for the production of the reaction product is not high enough and the alkyleneoxide adduction reaction velocity is not high enough. The compression strength and the dimensional stability of the polyurethane foam obtained by using the polyol obtained by the adduction of alkyleneoxide to the reaction product are not high enough.